1. Field of the Invention
The present invention relates generally to semiconductor device testing, and more particularly to the field of test head positioners or manipulators.
2. Description of Related Art
Typically, individual semiconductors or integrated circuit (IC) devices are formed on a semiconductor wafer in a matrix array, where each IC has a plurality of electrical contact portions or pads formed on the edge or surface of the IC. Moreover, both during and following fabrication, IC devices are automatically tested to determine whether their circuits meet design specifications. Such tests are generally carried out using a test head, otherwise known as a testing head, IC tester, or the like. In use, the test head is accurately aligned and docked with an IC device handler. The IC device handler then positions each IC device to be tested in a location where electrical contact can be made between the test head and the IC device. Testing then occurs to determine whether the IC device""s circuits meet design specifications.
To ensure a high throughput of IC devices being tested, the test heads typically test multiple IC devices simultaneously. Also, to increase the speed and accuracy of each test, the signal path between each IC device and the test equipment must be kept to a minimum. This requires a test head with a high density of sophisticated electronic components located close to the interface with the IC device handler. Consequently, test heads are very large and heavyxe2x80x94typically 300 kilograms or more.
This size and weight makes it difficult to manipulate or position the test head. During use it is often required to undock the test head from the IC device handler and move the test head to another location on the test facility floor. To accomplish the task of both moving the test head to another location on the test facility floor and accurately aligning the test head with an IC device handler, a test head positioner or manipulator is used. Examples of such test head manipulators can be found in U.S. Pat. Nos. 4,973,015; 5,241,870; 5,440,943; 5,450,766; 5,506,512; 5,606,262; 5,931,048; 5,949,002; 6,006,616; and 6,023,173, all of which are hereby incorporated by reference.
Most of these test head manipulators use counterweights, hydraulics, pneumatics, or electrical actuators to manipulate the test head and hold it in position. A disadvantage of counterweight systems is that the overall weight of the test head manipulator is significantly increased, adversely affecting its portability. Moreover, these test head manipulators are complex, necessitate additional structural, floor, and seismic tie-down support. These test head manipulators are also expensive to manufacture, ship, and use. They also incorporate stored energy that poses a potential safety hazard for users of the test head manipulators. Additionally, hydraulic systems pose cleanliness issues due to leakage.
Accordingly, a test head manipulator that is safe, simple, and inexpensive to make and use, and that does not require counterbalance weights, hydraulics, pneumatics, or locking mechanisms, would be highly desirable.
According to the invention there is provided a test head manipulator. The test head manipulator comprises at least one, but preferably two, bearings coupled to a stationary object, such as a frame. A lead screw that can rotate about its longitudinal axis, is positioned between the bearings. A non-translation mechanism is provided to prevent the lead screw from translating along its longitudinal axis. In a preferred embodiment, one of the bearings is a thrust bearing that provides the non-translation mechanism to prevent the lead screw from translating along its longitudinal axis. In this embodiment, the other bearing is preferably a radial bearing, which assures the alignment of the lead screw.
A lead nut is threaded onto the lead screw and is prevented from rotating about the longitudinal axis by a non-rotation mechanism. The non-rotation mechanism preferably includes a linear bearing slidingly coupled to a shaft, which is oriented substantially parallel to the lead screw""s longitudinal axis. The linear bearing is also rigidly coupled to the lead nut, thereby preventing rotation of the nut. Consequently, when the lead screw is rotated, the lead nut and linear bearing translate along the lead screw.
A carriage constrained to move along a vertical path is coupled to the lead nut by means of a cable and pulley system. The carriage is also configured to couple to an electronic test head.
In use, when the lead screw is rotated, the lead nut translates along the longitudinal axis, moving the cables and translating the carriage and test head along a vertical path.
The lead angle of the lead screw and lead nut is such that the lead screw cannot be turned by axial pressure on the lead nut. The test head can only be moved vertically by turning the lead screw, and thereby moving the lead nut. Since axial pressure on the lead screw by the lead nut cannot turn the lead screw, the lead nut and the coupled carriage and test head will be held in position without input.
In addition, the test head manipulator provides for rotational motion of the test head about two orthogonal axes. One of the axes has a worm drive mechanism (rotary drive) which facilitates rotational positioning of the test head. The lead angle of the worm gear is chosen such that the test head will be held in position without active input.
Accordingly, the present invention addresses the problems of the prior art by providing a safe, simple, and inexpensive test head manipulator.